Intraoperative 2D C-arm and 3D O-arm in children: a comparative phantom study

Abstract

Purpose: Exposure to ionizing radiation is a concern for children during intraoperative imaging. We aimed to assess the radiation exposure to the paediatric patient with 2D and 3D imaging.

Methods: To evaluate the radiation exposure, patient absorbed doses to the organs were measured in an anthropomorphic phantom representing a five-year-old child, using thermoluminescent dosimeters. For comparative purposes, organ doses were measured using a C-arm for one minute of fluoroscopy and one acquisition with an O-arm. The cone-beam was centred on the pelvis. Direct and scattered irradiations were measured and compared (Student's t-test). Skin entrance dose rates were also evaluated.

Results: All radiation doses were expressed in µGy. Direct radiation doses of pelvic organs were between 631.22 and 1691.87 for the O-arm and between 214.08 and 737.51 for the C-arm, and were not significant (p = 0.07). Close scattered radiation on abdominal organs were between 25.11 and 114.85 for the O-arm and between 8.03 and 55.34 for the C-arm, and were not significant (p = 0.07). Far scattered radiation doses on thorax, neck and head varied from 0.86 to 6.42 for the O-arm and from 0.04 to 3.08 for the C-arm, and were significant (p = 0.02). The dose rate at the skin entrance was 328.58 µGy.s^-1 for the O-arm and 1.90 with the C-arm.

Conclusion: During imaging of the pelvis, absorbed doses for a 3D O-arm acquisition were higher than with one minute fluoroscopy with the C-arm. Further clinical studies comparing effective doses are needed to assess ionizing risks of the intraoperative imaging systems in children.

Keywords: CBCT; O-arm; ionizing radiations; paediatric orthopaedics; patient exposure.

Fig. 1

Example of a phantom slice, showing different tissue densities, fixtures and thermoluminescent dosimeter placements with their associated number.

Fig. 2

Absorbed doses comparison for each organ between one 3D acquisition with the O-arm and one minute of fluoroscopy with the C-arm. Direct irradiation on the pelvic organs is coloured by red. Scattered irradiation on abdominal organs is coloured yellow and on thoracic and upper organs blue, with decreasing level respectively (R., right; L., left; PA, posteroanterior).

Fig. 3

Comparison of dose output (air kerma rate) at the skin surface with the O-arm in 2D mode and with the C-arm for both ten seconds of fluoroscopy (PA, posteroanterior; LAT, lateral).